In his commentary on the Book of Revelation, Andrew of Caesarea (6th–7th centuries) wrote:
The four animals and elders signify that from Angels and humans one flock and one Church was formed through Christ God, who united the divided and destroyed the barriers of the middle space. And so, as we have heard, together with the four animals, who surpass other ranks of Angels, the divine hymns and worship are also worthy of the elders, signifying the fullness of the saved.
In the Orthodox Church, the tetramorph of the evangelists is linked to the concluding words of the priest’s secret eucharistic prayer at the liturgy, which he proclaims as a chant during the service: “singing (eagle), crying out (ox), shouting (lion), and speaking (man).”
In the Orthodox Church, the first chapter of the Book of the Prophet Ezekiel, which narrates the mysterious four creatures bearing the throne of glory, is read at the sixth hour on Great Monday and Tuesday.”